More than 2,000 veterans were surveyed in 2011 and again in 2013. Each time they were asked whether they'd had suicidal thoughts in the past two weeks.

Nearly 4 percent reported suicidal thoughts in the first survey, about 5 percent reported such thoughts in the second survey, and about 5 percent reported suicidal thoughts in both surveys -- called chronic suicidal thinking. Overall, 13.7 percent reported suicidal thinking in one or both surveys, the researchers said in a VA media release.

A U.S. Centers for Disease Control and Prevention study published in 2011 found that 3.7 percent of American adults reported suicidal thoughts in the previous year.

The VA's findings show the need for ongoing monitoring of suicidal thoughts among veterans, not just a one-time screening, the researchers said. They were led by Noelle Smith, who conducted the study while with the VA Connecticut Healthcare System. She is now at the James A. Haley Veterans Hospital in Tampa, Fla.

Among veterans who reported suicidal thoughts in the second survey, 65 percent had never gotten any mental health treatment. That finding shows the need for more outreach, the study authors said.

Mental distress, physical health problems and drug and/or alcohol use were associated with chronic suicidal thinking, while social connectedness was linked with a reduction in suicidal thoughts.

The results underscore the need to treat veterans' mental and physical health problems and increase their sources of social support to prevent and reduce suicidal thoughts, the researchers said.

The study is available online and is to appear in the June print issue of the Journal of Affective Disorders.